Polymer and small molecule based hybrid light source

#1. Field of the Invention

#This invention relates generally to the art of thin film device processing and fabrication. More specifically, the invention relates to the structure of Organic Light Emitting Diode devices and displays.

#2. Related Art

#FIG. 1 shows a cross-sectional view of an embodiment of an EL device 205 according to at least one embodiment of the invention.

#FIG. 2 shows a cross-sectional view of an embodiment of an electroluminescent (EL) device 305 according to at least one embodiment of the invention.

#In one or more embodiments of the invention, what is disclosed is a novel hybrid electroluminescent (EL) device primarily based on solution-processed polymer active layers, including a polymer-based light emitting layer but incorporating an additional small molecule layer fabricated on the top of the polymer-based light emitting layer. In some embodiments, the small molecule layer is fabricated by thermal evaporation techniques. The present invention is motivated in the design of organic light sources to obtain high efficiency, with desired emission spectra. One novel aspect of the invention includes incorporation of an additional emissive small molecule-based layer above the polymer-based active region in a polymer based lighting device such as an OLED. In this way, the color spectrum can be easily be tuned as desired by adding just one extra deposition step. The remaining device structure is still fabricated using advantageous solution processing techniques.

#In accordance with one embodiment of the invention, the structure of a novel hybrid organic electroluminescent device comprises of an anode (e.g. indium-tin-oxide (ITO)), an anode buffer layer (e.g. PEDOT:PSS (polyethylenedioxythiopene), PANI (conducting polyaniline)), a hole transporting interlayer (e.g. an amine-based organic material), a polymer-based light emissive layer (this layer can be doped with additional carrier transport and emitting moieties), a small molecule-based light emissive layer and a cathode layer (e.g. barium covered with aluminum). The function of the anode buffer layer is to provide efficient hole injection into subsequent layers and also acts as a buffer layer to smooth the surface of the anode and to provide a better adhesion for the subsequent layer. The function of the hole transporting interlayer is to transport holes, injected from the anode buffer layer, to the polymer-based light emissive layer, where recombination with electrons will occur and light will be emitted. The hole transporting interlayer usually consists of a high hole mobility organic material, such as TPD, NPD, amine-based starburst compounds, amine-based spiro-compounds and so on. Another function of the hole transporting interlayer is to move the recombination zone away from the interface with the anode buffer layer. In alternate embodiments of this invention, the hole transporting interlayer may be excluded from the device structure. The function of the polymer-based light emissive layer is to transport both types of carriers and to efficiently produce light of desirable wavelength from electron-hole pair (exciton) recombination. The function of the small molecule-based light emissive layer is to transport both types of carriers and to efficiently produce light which complements the emission of the polymer-based light emissive layer. The function of the electron injection layer is to efficiently inject electrons into the electroluminescent layer. The small molecule-based light emissive layer can be emissive and also serve the role of hole blocking.

#OLED device 205 includes substrate 208 and a first electrode 211 on the substrate 208. The first electrode 211 may be patterned for pixilated applications or un-patterned for backlight or other general lighting applications. The OLED device 205 also includes a semiconductor stack 214 on the first electrode 211. The semiconductor stack 214 includes at least the following: (1) an anode buffer layer (ABL) 215, (2) a polymer-based light emissive layer (EML) 216 and (3) a small molecule-based light emissive layer (SMEML) 220.